1. Field of the Invention
The present invention relates to a preform usable in molding a container such as intravenous drip bottle, said container having a hanger which is used to hang the container upside down. The present invention also concerns a method of molding such a container.
2. Description of the Related Art
The molding of such a container requires an additional step of forming the hanger in addition to the conventional molding steps of injection molding a preform and stretch blow molding the preform into the final shape. On the other hand, it has been required to simplify the molding process for reducing the manufacturing cost. In addition, the hanger in such a container is required to have a high reliability since if the container is used as an intravenous drip bottle, any accidental separation of the hanger from the container body may affect the life of a patient.
Many proposals have been made to mold these containers having hangers. Prom the standpoint of the safety, it is desirable to injection mold a container body and a hanger as an integral unit. Some such proposals are disclosed in Japanese Patent Laid-Open Nos. Sho 62-273822. Sho 62-273823 and Sho 63-11324. These Laid-Open applications describe a process of injection molding a preform, the bottom of the preform being formed integrally with a perforated or non-perforated hanger. The hanger is formed into a flat plate having a given thickness. As seen from the figures in each Laid-Open application, the connection between the container bottom and the hanger is in the form of a flat connecting piece having a given thickness and a width which is substantially equal to the diameter of the preform.
However, such a type of container having a hanger has not been put to practical use for the following possible reasons.
The injection molding is accomplished by injecting a molten plastic material into the mold cavity through a gate which is formed to connect with the central bottom end portion of the hanger. The molten plastic material will flow from the first cavity region in which the hanger is to be molded through the second cavity region in which said connecting piece of rectangular cross-section having a narrow width is to be molded into the third or final cavity region in which the cylindrical bottomed barrel of the container is to be molded.
With the conventional formation of a preform having no hanger, the plastic material flows into the final cavity region directly through the gate. This is very different from the formation of a preform having a hanger. In the latter case, the molten plastic material tends to flow into a particular circumferential position in the third cavity region (which is directly above the connecting piece) more easily since the material flows into the final cavity region through the second cavity region which is used to mold the connecting piece of rectangular cross-section having the reduced width. Thus, the flow velocity of the molten plastic material becomes irregular through the circumferential positions of the preform barrel. This results in unevenness or deviation in temperature at the circumferential positions of the preform barrel. If a perform having such a deviation in temperature is biaxially stretched and blow molded, the wall-thickness of the circumferential side wall of the molded container will be uneven throughout.
It is further desirable that a hinge member permitting the hanger to be folded or bent is formed between the hanger and the bottom wall of the container. In such a case, the prior art injection molds a hinge member having a reduced wall-thickness at the proximal end of the connecting piece adjacent to the bottom wall of the preform. As shown in Japanese Patent Laid-Open No. Sho 62-273822. However, this results in reduction of the size of the entrance for moving the molten plastic material into the barrel of the preform. Thus, the material will be cooled at the thinner hinge portion. As a result, the molten plastic material is prevented from flowing into the final or container barrel molding cavity region. This leads to failure in molding and greatly decreases the number of suitable containers.